This invention relates to the treatment of vegetable materials with a view to reducing the content of certain undesirable substances, particularly caffeine and chlorogenic acid.
For some time now, efforts have been made to find an industrial method for decaffeinating vegetable materials, particularly coffee, which does not involve the use of organic solvents. The techniques currently used in industry for decaffeination use organic solvents, such as trichlorethylene, methylene, chloride, chloroform, etc., the caffeine being extracted by contacting the vegetable material itself or an extract thereof with these solvents which, laden with caffeine, have to be subsequently separated.
These solvent extraction techniques are attended by numerous disadvantages. The operational burden associated with the treatment and recycling of these solvents is considerable. Being volatile and toxic, they necessitate expensive safety measures and have to be carefully eliminated from the beverage. Finally, they solubilise non-selectively a certain number of desired constituents of the beverage which often has to be isolated and reincorporated in the product after decaffeination.
In order to eliminate these disadvantages, several attempts have been made to effect decaffeination by other means.
For example, French Pat. No. 698,118 describes the use of active carbon or silica for eliminating the caffeine and other undesirable elements from an aqueous extract. However, other interesting soluble constituents of the coffee are also adsorbed and the difficult regeneration of the adsorbent cannot be carried out on an industrial scale.
According to U.S. Pat. No. 3,108,876, a coffee liquor may be decaffeinated by using ion exchange resins. The disadvantage of this method is the simultaneous adsorption of other interesting constituents, the demineralisation and the reduction in pH of the liquor. The liquor has to be subsequently neutralised to increase its pH-value to an acceptable level and to restore the mineral substances.
Published French Patent Application No. 2,297,004 relates to a process for decaffeinating an aqueous extract of a vegetable material by adsorption on neutral polymer resins. The disadvantage of this method is that, in addition to the caffeine, it adsorbs certain interesting soluble constituents of which the recovery necessitates treatment with a water/alcohol mixture, followed by subsequent washing of the resin.
Another process, which is described in published French Patent Application No. 2,231,407, sets out to fix a substance to be separated from an aqueous medium, for example caffeine, on a macromolecular substance in the liquid state and subsequently to separate the aggregate formed by ultra-filtration on a semi-permeable membrane. However, this method has not so far been accepted for industrial application.